Logo
FULL SITE MENU

2004 Honda BF50 tach problem

Z

zick

New member
I bought a pontoon last season that came w/ what I thought was a bad Tach. It was originally a Faria tach w/o the hour meter.
It was very errartic, jumping all over the place and never going over 3500rpms.
So I found the part number and ordered a brand new one. But the problem still continued.

I've read all the threads I could find on this problem and can't figure it out.
http://www.marineengine.com/boat-forum/showthread.php?393623-Honda-BF50-Tach-Help-Solve-this-mystery
I haven't fully tested the charging system but my volt gauge and battery show good voltage.
I haven't bought the resistor assembly talked about in the above post because it's suppose to only be for tachs w/ the hour meter which I don't have. I did however try some diodes in the same placement as the resistor assemble as a cheap test. It helped reduce the tach jumpiness but still doesn't go over 3500.

The one thing that I figured out right at the end of the season was that the Tach actually worked correctly when I was running the trim motor. E.G. I could be running WOT and the tach would only show ~3500, but as soon as I hit the trim, it jumps to ~5800 and would stay there until I let go of the trim button.

Anyone know why this might be happening?
 
Since you must have some knowledge of diodes, etc. Get a 100 ohm resistor (not sure what the wattage should be) and put it across the grey tach lead and the black (ground). See if it helps. For a test, it should not matter what the wattage is but Radio Shack does sell a 5 watt for about $1. http://www.radioshack.com/product/index.jsp?productId=12448372

If you do have a 2004, the tach lead comes from the rectifier. The tach acts up due to the tach being "overdriven"....like someone with a 100 watt amplifier blasting music into a little 4 inch speaker...total distortion.

The resistor is supposed to shunt the excess to ground and smooth things out.

It is worth a try.

Why would your trim let it operate differently? My theory ...when you hit your trim button, the voltage and current going to rectifier reduces. Therefore, the output should be reduced, which should also reduce the overdrive voltage. As I said, it is just a guess.

Mike
 
Hi Mike,
I was hoping you'd reply.

Unfortunately I already tried placing some diodes between the grey and black connections as memtioned before.
Can't remember exactly which ohms I got (pretty sure it was the 100, I'll try and double check when I get home tonight) and while it did smooth the jumpiness (doesn't bounce around as bad), it still didn't allow it to get up to full RPM (unless trim was operated). I even tried doubling up the diodes but no real help.
Oh and no my knowledge of diode is very limited, it's just enough to get me into trouble. :D

I keep thinking the resistor pack may magically fix it but I really don't want to waste money if it doesn't work.


Thanks for your help!
 
When you say diode, do you mean resistor? They are not the same thing and do not work the same.

Make sure that you tried using a resistor.

Not to be negative, but as you pointed out, you do not have the tach with the hour meter and it probably will not work.

MAKE SURE THAT THE TACH IS SET ON #2.

That being said...I have been thinking a little more about how it "worked" when trimming. Besides possibly reducing voltage coming out of the rectifier on the tach lead, the 12v, that powers the tach, may have reduced, helping the problem, for some reason.
If you have a voltmeter on your dash, how much does the reading change when you trim the motor? For example..does the voltage drop from 13v to 11v?

If so, then maybe we can come up with something that will reduce the power to the gauge and fool it. I am thinking a different resistor in series in the 12v to the gauge. But, I have to know how much voltage to drop it before I can suggest a resistor value.

Of course, if we drop the voltage to the gauge, what will it do when you trim (causing even less voltage to the gauge). Who knows?

Keep in mind, the last part of this post is pie in the sky thinking. I have never gone down this path, since I know the tach with hour meter works, I just put one in. As I have said in other posts, neither Faria or Honda can explain why the tach with hour meter works and the tach without hour meter does not. They are certainly not going to provide any input on what we may be attempting....so we are on our own...if you are willing to do some experimentation.

Mike
 
Sorry, meant to say resistor.
These are the ones I tried. Wasn't sure on the exact sizing so I just picked these up.
http://www.radioshack.com/product/index.jsp?productId=2062323

And I did try all the settings on the tach and I'm on #2 now.

I'll have to try and get a voltage reading when running the trim but it maybe a while as the boat is still in storage (stupid winter just won't go away fast enough).
Sorry, this post was probably a little pre-mature. I just happened to be pulling the carbs for a rebuild and got thinking about the tach issue.

Thanks
 
The resistor that you used is a 1000 ohm, if it is the one that you linked to. If you have 10 of them in parallel, that would make 100 ohms.

So, when you get back to it, get a 100 ohm and try it. A 100 ohm resistor will make a big difference from a 1000 ohm in this case.

Mike
 
Thanks,
Like I said, I know just enough to get me into trouble. I was thinking about it backwards. I thought the 1000 ohm resistor would be more resistant than the 100 ohm resistor.
I will try and find a 100 ohm resistor and try again.

Thanks for your help!
 
You are right...it does have more resistance, but when you put a high or relatively high resistor in parallel with the gauge, it has minimal shunting ability. It lets less current bypass through it.

Put a lower value resistor in shunt and it will allow more current to bypass through it.

At least that is what "Mr Wizard" said.

Mike
 
Back
Top